<style>
    .coordinates {
        background: rgba(0, 0, 0, 0.5);
        color: #fff;
        position: absolute;
        bottom: 40px;
        left: 10px;
        padding: 5px 10px;
        margin: 0;
        font-size: 11px;
        line-height: 18px;
        border-radius: 3px;
        display: none;
    }
</style>

<div id="map"></div>
<pre id="coordinates" class="coordinates"></pre>

<script>
    var coordinates = document.getElementById('coordinates');
    var map = new mapboxgl.Map({
        container: 'map',
        style: 'mapbox://styles/mapbox/streets-v11',
        center: [0, 0],
        zoom: 2
    });

    var marker = new mapboxgl.Marker({
        draggable: true
    })
        .setLngLat([0, 0])
        .addTo(map);

    function onDragEnd() {
        var lngLat = marker.getLngLat();
        coordinates.style.display = 'block';
        coordinates.innerHTML =
            'Longitude: ' + lngLat.lng + '<br />Latitude: ' + lngLat.lat;
    }

    marker.on('dragend', onDragEnd);
</script>
